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Activity Funded

Testing the efficiency of the Diatom Biological Pump for the last 40 kyrs

A Eficiência do Bombeamento Biológico por Diatomáceas nos últimos 40 000 anos

Reference
2023.11539.PEX
Project Start Date
2025-02-20
Project End Date
2027-02-19
Principal Investigator
Scientific Area
Natural sciences
Funding Program
Concurso de Projetos Exploratórios em Todos os Domínios Científicos 2023

Abstract

Diatoms play a major role in the global carbon cycle and climate through their prominent role in the biological pump: they transport 20% of the carbon from the atmosphere to the deep ocean (Tréguer et al., 1995). The present ongoing climate warming and continuous increase in atmospheric CO2 (pCO2) leads to acidification and stratification of the surface ocean where the diatoms live. It is crucial to understand how these environmental changes may affect diatoms and their role in carbon sequestration. Recent diatom experiment in the Southern Ocean - SO (Petrou et al. 2019) shows that ocean acidification reduces the contribution of large heavily silicified diatom species, which contain high organic carbon, and increases the presence of smaller and thinner species. Such results raise a major question: will ocean acidification result in SO diatoms removing less carbon from the atmosphere than expected, worsening the already dramatic climate projections? A possible way to elucidate such an urgent issue is to reconstruct changes in diatom assemblages in sediments from the Drake passage (SO) representing different past conditions ofoceanic acidity to explore the relationship between diatom assemblage and pH through time. A boron isotopic record on corals, a proxy for water acidity, is available at this site for the last 40,000 years (Rae et al., 2018) and diatoms are particularly abundant in the SO where dissolved silica in the surface water is plentiful. The SO plays a critical role in pCO2 dynamics by releasing carbon through upwelling (Toggweiler, 1999) and by absorbing pCO2 via diatom production and the subduction of intermediate and mode waters, turning the SO into a major sink for carbon (Sabine et al., 2004). Through upwelling, dissolved inorganic carbon rich water of the North Atlantic Deep Water (NADW) reaches the surface, releasing carbon to the atmosphere (Toggweiler and Samuels, 1995). The Antarctic Intermediate Water (AAIW) is principally made of this upwelled water which was later under high wind speeds stress, promoting gas transfer and CO2 sequestration (Sabine et al. 2004). AAIW flows northward at intermediate depth and constitutes a major supplier of the Atlantic Meridional Overturning Circulation (AMOC) return pathway (e.g. Schmitz Jr. and McCartney, 1993). Its northward expansion through the Atlantic possibly indicates AMOC strength (Came et al., 2008; Xie et al., 2012) and this water mass which is nutrient rich is likely to promote primary production at key-locations of the North Atlantic (Sarmiento et al., 2004). The AMOC strength has already been related to past abrupt climate changes (Lynch-Stieglitz, 2017), and at Present, its relatively recent slowdown (Rahmstorf et al. 2015; Caesar et al., 2021) has been linked to the recent climate warming, with climate model projections of a 2ºC temperature increase predicting catastrophic climatic conditions directly affecting societies either through super-storms or ice melt leading to sea level rise (Hansen et al., 2016). Hence, a better understanding of SO processes affecting surface water acidity and AAIW export is critical for assessing the impact of a warming climate on AMOC strength and carbon sequestration. In order to also assess the northward progression of AAIW into the North Atlantic, a sediment core from the subtropical North Atlantic (Corner Rise seamounts area) will be investigated for its diatom content since diatom production at this site is linked to shallower AAIW at times of weak AMOC. Indeed, an exceptionally preserved diatom production record possibly related to AAIW has been recorded at a nearby location during Heinrich Event 1 (Gil et al., 2009), a period of massive icebergs discharge into the North Atlantic that markedly perturbed AMOC (McManus et al., 2004). A record of 231Pa/230Th will also be generated as a proxy for AMOC strength. Studying both sites (Drake passage and Corner rise) will allow to investigate critical changes in ocean circulation in relation to pCO2. The project participants have extensive expertise in diatom taxonomy and statistical treatment of micropaleontological data (Abrantes et al., 2005, Gil et al., 2009, 2015, 2018) as well as 231Pa/230Th systematics (McManus et al., 2004; Henry et al., 2016) which will guarantee the success of the project and the ability to expand their skills into a new oceanic setting such as the SO.

Institutions

Main Institutions

  • Instituto Português do Mar e da Atmosfera (IPMA)

Other Institutions

  • Columbia University Lamont-Doherty Earth Observatory (LDEO)

Funding 50.000,00 €

Fundação para a Ciência e a Tecnologia (FCT) - Portugal

50.000,00 €